Burning behavior of an ethanol pool fire, increased by bubble behavior during sub-cooled nucleate boiling regime is investigated in this study. Different from traditional pool fires, a metal element - which consists of a thin cylindrical collector in the flame zone and a cylindrical disk immersed in the pool is used to further increase the heat transfer. During burning, heat is transferred from the cylindrical collector to the disk immersed in ethanol. The immersed element quickly exceeds the saturation temperature of ethanol and bubbles begin to form on its surface. This bubble behavior is carefully examined and bubble size, departure frequency, and overall dynamics are presented in this study. The behavior of bubbles changes with the initial immersion depth l of the element and similarly the overall mass burning rate of the ethanol pool also varies. Results show a nonlinear variation of mass loss rate with the increase of l, and regimes based on the bubble dynamics during the burning are identified for the first time.